To determine the independent effects of age and gender on the left ventricular response to upright cycle exercise, we analyzed gated blood pool scans at rest and maximal upright cycle exercise in 95 men and 50 women ages 23-86 yrs free of heart disease by history, physical exam, rest and exercise ECG and if > 40 years old, exercise thallium scan. Maximal cycle workload declined similarly with age in men (41%) and women (47%) between the third and the ninth decades, although the absolute maximal load achieved was higher in men for any given age, at seated rest age-associated declines in heart rate (HR) and increases in systolic blood pressure (SBP) were observed. Resting end diastolic volume index (EDVI) and stroke volume index (SVI) rose with age in men but not in women. In both sexes, maximal heart rate, ejection fraction and cardiac index declined with age whereas end systolic volume index (ESVI) and total systemic vascular resistance (TSVR) increased. Although EDVI at maximal effort increased with age in men but not in women, SVI was not age related with either sex. At a fixed external workload of 50 watts, heart rate decreased decreased and EDVI, ESVI, and SVI increased with age in men but not in women. At 50% of maximal effort, both sexes showed age-associated declines in heart rate, ejection fraction and cardiac index but increases in TSVR. Cardiac volumes were unrelated to age in women whereas both EDVI and ESVI increased with age in men at this relative workload. When men and women younger than 40 years who achieved similar maximal workloads of 125-150 watts were compared across workloads, women had higher heart rates and thence higher cardiac indices than their male counterparts whereas the men had higher systolic blood pressure responses. Fitness-matched older (>60 years) men and women demonstrated similar exercise hemodynamics except for a higher heart rate response in the latter.